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Tests - VirologicalTests An Overview 1.DirectExamination...

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Virological Tests An Overview
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Diagnostic Methods in Virology 1. Direct Examination 2. Indirect Examination (Virus Isolation) 3. Serology
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Direct Examination 1. Antigen Detection immunofluorescence, ELISA etc. 2. Electron Microscopy morphology of virus particles immune electron microscopy 3. Light Microscopy histological appearance inclusion bodies 4. Viral Genome Detection hybridization with specific nucleic acid probes polymerase chain reaction (PCR)
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Indirect Examination 1. Cell Culture cytopathic effect (CPE) haemabsorption immunofluorescence 2. Eggs pocks on CAM haemagglutination inclusion bodies 3. Animals disease or death  
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Serology Detection of rising titres of antibody between acute and convalescent stages of infection, or the detection of IgM in primary infection.                 Classical Techniques Newer Techniques 1. Complement fixation tests (CFT) 1. Radioimmunoassay (RIA) 2. Haemagglutination inhibition tests 2. Enzyme linked immunosorbent assay (EIA) 3. Immunofluorescence techniques (IF) 3. Particle agglutination 4. Neutralization tests 4. Western Blot (WB) 5. Counter-immunoelectrophoresis 5. RIBA, Line immunoassay
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Virus Isolation Cell Cultures are most widely used for virus isolation, there are 3 types of cell cultures: 1. Primary cells - Monkey Kidney 2. Semi-continuous cells - Human embryonic kidney and skin fibroblasts 3. Continuous cells - HeLa, Vero, Hep2, LLC-MK2, MDCK Primary cell culture are widely acknowledged as the best cell culture systems available since they support the widest range of viruses. However, they are very expensive and it is often difficult to obtain a reliable supply. Continuous cells are the most easy to handle but the range of viruses supported is often limited.  
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Cell Cultures Growing virus may produce 1. Cytopathic Effect (CPE) - such as the ballooning of cells or syncytia formation, may be specific or non-specific. 2. Haemadsorption - cells acquire the ability to stick to mammalian red blood cells. Confirmation of the identity of the virus may be carried out using neutralization, haemadsorption-inhibition or immunofluorescence tests.
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Cytopathic Effect (1) Cytopathic effect of enterovirus 71 and HSV in cell culture: note the ballooning of cells . (Virology Laboratory, Yale-New Haven Hospital, Linda Stannard, University of Cape Town)
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Cytopathic Effect (2) Syncytium formation in cell culture caused by RSV (top), and measles virus (bottom). (courtesy of Linda Stannard, University of Cape Town, S.A.)
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Haemadsorption Syncytial formation caused by mumps virus and haemadsorption of erythrocytes onto the surface of the cell sheet. (courtesy of Linda Stannard, University of Cape Town, S.A.)
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Problems with cell culture Long period (up to 4 weeks) required for result. Often very poor sensitivity, sensitivity depends on a large extent on the condition of the specimen.
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